Semiconductor integrated circuit and method for forming the same

ABSTRACT

In forming a thin film transistor (TFT), a semiconductor region is formed on a glass substrate and then a gate electrode is formed on the semiconductor region through an gate insulating film. After the gate electrode and a gate electrode arrangement extended from the gate electrode is anodized, insulators each having approximately rectangular shape are formed on side surfaces of the gate electrode and the gate electrode arrangement. An interlayer insulator is formed on a whole surface, and then the second layer arrangement is formed on the interlayer insulator. In an overlap portion in which the second layer arrangement overlaps the gate electrode and the gate electrode arrangement, since the insulators is formed, a slope is small.

This application is a Divisional of application Ser. No. 08/999,703,filed Feb. 5, 1997; which itself is a Continuation of application Ser.No. 08/431,323 filed Apr. 28, 1995, abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an integrated circuit in which a thinfilm insulated gate semiconductor device (thin film transistor, TFT) isformed on an insulating substrate and a method for the same. Theinsulating substrate represents an object having an insulating surfaceand includes an insulating material such as a glass and an object inwhich an insulator layer is formed on a material such as a semiconductoror a metal. In particular, the present invention relates to anintegrated circuit using a material containing mainly a metal materialsuch as aluminum, tantalum and titanium as a material of a gateelectrode arrangement. A semiconductor integrated circuit of the presentinvention is used in an active matrix circuit and a peripheral drivercircuit of a liquid crystal display or the like, a driver circuit of animage sensor or the like, an SOI integrated circuit, or a conventionalsemiconductor integrated circuit such as a microprocessor, amicrocontroller, a microcomputer, or the a semiconductor memory.

In a case wherein an active matrix type liquid crystal display device,an image sensor or the like is formed on a glass substrate, a structureconstructed by integrating thin film transistors (TFTs) is well known.In this structure, generally, after the first layer electrodearrangement (wiring) having a gate electrode is formed, an interlayerinsulator is formed and then the second layer electrode arrangement isformed. If necessary, the third and fourth layer electrode arrangementsare formed. In particular, in order to reduce a resistance of anarrangement, a metal material such as aluminum, tantalum and titanium isused as a material of each layer arrangement.

In an integrated circuit using TFTs, the second layer electrodearrangement is disconnected (broken) in an cross section portion (anoverlap portion) of an electrode arrangement (gate wiring) extended froma gate electrode and the second layer electrode arrangement. This isbecause it is difficult to form an interlayer insulator on a gateelectrode/arrangement with a superior step coverage and furtherplanerize it.

FIG. 4 shows a disconnection state in a conventional TFT integratedcircuit. In FIG. 4, a TFT region 401 and a gate electrode arrangement402 is formed on a substrate, and an interlayer insulator is formed tocover the TFT region 401 and the gate electrode arrangement 402. If thegate electrode arrangement 402 has a sharp edge, it cannot besufficiently covered with the interlayer insulator 403. In this state,when a second layer electrode arrangements 404 and 405 are formed, thesecond layer electrode arrangement 405 is disconnected in an overlapportion 406.

In order to prevent such disconnection, it is necessary to increase athickness of a second layer electrode arrangement (wiring). For example,it is desired that the thickness of the second layer electrodearrangement is about twice as thick as a thickness of a gate electrodearrangement. However, by increasing a thickness of the second layerelectrode arrangement, a difference between a concave and a convexfurther increases in an integrated circuit. Also, when a further layerelectrode arrangement is formed on the second layer electrodearrangement, a thickness of the second layer electrode arrangement mustbe determined in consideration of the disconnection. It is impossible toform a circuit in which an integrated circuit having an uneven surfaceis not desired, such as a liquid crystal display device, by increasing athickness of the second layer electrode arrangement.

In an integrated circuit, if the disconnection occurs, since a wholecircuit is defect, it is important to decrease the frequency of thedisconnection.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above problems, thatis, to decrease the frequency of the disconnection, thereby to increasea yield of an integrated circuit.

In the present invention, an oxide film is formed on at least uppersurface of a gate electrode arrangement by oxidizing a gate electrodeusing anodization. Further, after insulators (side walls) having asubstantially rectangular shape are formed on side surfaces of the gateelectrode arrangement by anisotropy etching, an interlayer insulator isdeposited and then the second layer electrode arrangement is formed. Itis necessary not to etch easily the oxide film formed by anodization incomparison with a material constructing a side wall which is formedlater. When side walls are formed using a silicon oxide, an aluminumoxide, a tantalum oxide, a molybdenum oxide, a tungsten oxide or thelike is preferred. These material have an extremely low etching rate ina case wherein a silicon oxide is etched by dry etching using an etchinggas including fluorine such as NF₃ and SF₆.

In a method of an embodiment according to the present invention, anisland semiconductor layer is formed, and then a film is formed as agate insulating film on the island semiconductor layer. Also, a gateelectrode/arrangement are formed. It is required that the gateelectrode/arrangement are formed using a material to be anodized and afilm obtained by anodization is not etched easily in comparison with aside wall.

After that, the gate electrode/arrangement are immersed into anelectrolytic solution having approximately neutral to apply a positivevoltage to it, so that an anodic oxide film is formed on at least uppersurface of the gate electrode/arrangement. This process may be performedby vapor phase anodization. This is the first stage.

An insulating film is formed to cover the gate electrode arrangement andthe surrounding anodic oxide film. In this film formation, coverage isimportant. Also, it is suitable that a thickness of the insulating filmis about ⅓ to 2 times as thick as a thickness (height) of a gateelectrode/arrangement. It is preferred to use chemical vapor deposition(CVD) such as plasma CVD, low pressure CVD, atmosphere pressure CVD orthe like. Such formed insulating film is etched by anisotropy etching inan approximately vertical direction to a substrate. In etchingcompletion, although the insulating film in an even portion is etched,the gate insulating film formed under the insulating film may be etched.As a result, in a step portion (a difference in height) such as sides ofthe gate electrode/arrangement, since the insulating film is thick,insulators (side walls) having a substantially rectangular shape remain.This is the second stage.

After an interlayer insulator is formed, a contact hole is formed in atleast one of source and drain regions of a TFT, and then a second layerelectrode arrangement is formed. This is the third stage.

In the above stages, there is several cases for doping to form sourceand drain regions of a TFT. When only N-channel type TFT is formed on asubstrate, an N-type impurity having a relatively high concentration maybe introduced into a semiconductor layer using the gate electrode andthe surrounding anodic oxide film as masks in a self-alignment in qprocess between the first and second stages. When an anodic oxide filmis formed on side surfaces of the gate electrode, so-called offset gatetype TFT in which the source and drain regions are spaced apart from thegate electrode by a thickness of the anodic oxide film is obtained. Asdescribed below, a normal TFT includes such TFT.

When an N-channel type TFT having a low concentration drain (lightlydoped drain, LDD), an LDD type TFT is formed, after an impurity having arelatively low concentration is introduced into a semiconductor layer ina process between the first and second stages, an N-type impurity havinga higher concentration is introduced in the semiconductor in aself-alignment using a gate electrode and side walls as masks. A widthof an LDD region is approximately equal to that of the side walls. Whenonly P-channel type TFT is formed, the above process may be performed.

Also, a complementary type circuit (CMOS circuit) having N-channel typeand P-channel type TFTs can be formed by the above process. When bothN-channel type and P-channel type TFTs are constructed by using a normalTFT or an LDD type TFT, an impurity introduction for forming only one ofN-channel type and P-channel type TFTs may be used with respect to anN-type impurity and a P-type impurity.

When an N-channel type TFT necessary to prevent a hot carrier is formedas an LDD type TFT and a P-channel type TFT unnecessary to prevent a hotcarrier is formed as a normal TFT, a special impurity introductionprocess is performed. In this process, an N-type impurity having arelatively low concentration is introduced into a semiconductor layer ina process between the first and second stages. This is the firstimpurity introduction. In this state, an N-type impurity may beintroduced in a semiconductor layer of the P-channel type TFT.

Further, using the semiconductor layer of the N-channel type TFT as amask, a P-type impurity having a high concentration is introduced intoonly the semiconductor layer of the P-channel type TFT. This is thesecond impurity introduction. Even though the N-type impurity isincluded in the semiconductor layer of the P-channel type TFT by theabove N-type impurity introduction, since the P-type impurity having ahigher concentration is introduced by the P-type impurity introduction,a conductivity type of a semiconductor is a P-type. A concentration ofthe impurity introduced by the second impurity introduction is higherthan that of the impurity introduced by the first impurity introduction,by preferably 1 to 3 orders (digits).

Finally, in order to form the source and drain regions of the N-channeltype TFT, an N-type impurity having a relatively high concentration isintroduced in a process between the second and third stages. This is thethird impurity introduction. In this state, the impurity introductionmay be performed using a mask in order not to introduce the N-typeimpurity into the P-channel type TFT, or a mask may be not used. Whenthe mask is used, it is required that a concentration of the N-typeimpurity to be introduced is lower than that of a P-type impurityintroduced by the second impurity introduction, and the concentration ofthe N-type impurity is preferably {fraction (1/10)} to ⅔ of that of theP-type impurity. As a result, the N-type impurity is also introducedinto the P-channel type TFT. However, since the impurity concentrationis lower than that of the P-type impurity, a P-type is maintained.

In the present invention, step coverage of an interlayer insulator in anoverlap portion of gate electrode arrangements is improved by sidewalls, so that the frequency of disconnection of the second layerelectrode arrangement can be decreased. Also, an LDD structure can beobtained using the side walls.

In the present invention, an anodic oxide film is important. In thesecond stage, anisotropy etching is performed to form side walls.However, since it is difficult to control a plasma in an insulatingsurface, variations of etching (depth) within a substrate produce. Ifthe anodic oxide film is not formed on an upper surface of a gateelectrode, the gate electrode may be etched largely (deeply) in aportion on the same substrate. On the other hand, if the anodic oxidefilm is formed, etching is stopped, so that the gate electrode isprotected.

In the present invention, after the formation of a gateelectrode/arrangement, an oxide film having a thickness of 1000 Å ormore, preferably 1500 to 4000 Å is formed on at least upper surface(preferably, upper and side surface) of the gate electrode/arrangementby oxidizing the gate electrode/arrangement using anodization, and thena silicon nitride film is formed on upper and side surfaces of the oxidefilm by plasma CVD and sputtering. Further, after insulators (sidewalls) having a substantially rectangular shape are formed on sidesurfaces of the gate electrode arrangement by anisotropy-etching aninsulator to be formed, an interlayer insulator is deposited and thenthe second layer electrode arrangement is formed. In a case wherein asilicon oxide as a material constructing side walls is etched by dryetching, since an etching rate of a silicon nitride is small, thesilicon nitride can be used as an etching stopper.

When a silicon nitride film and a silicon oxide film are formed, it isnecessary to use 200° C. or higher, in particular, 300° C. or higher (ina silicon nitride film). When a material such as aluminum, tantalum,titanium is used as a gate electrode/arrangement, since an unevenportion (hillock) produces on a surface at such temperature, this causesa short circuit in an interlayer. If a desired impurity is introducedinto the metal material, production of the hillock can not be preventedcompletely. In order to prevent completely the production of thehillock, it is preferred that a surface is covered with an anodic oxidefilm having a thickness of 1000 Å or more. Therefore, the gateelectrode/arrangement is oxidized by the above anodization to form anoxide film on a surface of the gate electrode/arrangement.

In a method of an embodiment according to the present invention, anisland semiconductor layer is formed, and then a film is formed as agate insulating film on the island semiconductor layer. Also, a gateelectrode/arrangement are formed. It is required that the gateelectrode/arrangement are formed using a material to be anodized.

After that, the gate electrode/arrangement are immersed into anelectrolytic solution having approximately neutral to apply a positivevoltage to it, so that an anodic oxide film is formed on at least uppersurface of the gate electrode/arrangement. This process may be performedby vapor phase anodization.

A silicon nitride film having a thickness of 100 to 2000 Å, preferably200 to 1000 Å, is formed. The film formation may be performed by anotherCVD, sputtering or the like. This is the first state.

An insulating film is formed on the silicon nitride film. In this filmformation, coverage is important. Also, it is suitable that a thicknessof the insulating film is about ⅓ to 2 times as thick as a thickness(height) of a gate electrode/arrangement. It is preferred to usechemical vapor deposition (CVD) such as plasma CVD, low pressure CVD,atmosphere pressure CVD or the like. Such formed insulating film isetched by anisotropy etching in an approximately vertical direction to asubstrate. In etching completion, although a surface of the siliconnitride film is etched, the gate electrode and the gate insulating filmwhich are formed under the silicon nitride film is not etched. As aresult, in a step portion (a difference in height) such as sides of thegate electrode/arrangement, since the insulating film is thick,insulators (side walls) having a substantially rectangular shape remain.This is the second stage.

After an interlayer insulator is formed, a contact hole is formed in atleast one of source and drain regions of a TFT, and then a second layerelectrode arrangement is formed. This is the third stage.

After side walls are formed in the second stage, a silicon nitride filmmay be etched by dry etching. It is further preferred to perform thisetching while observation by an end point monitor. In the etchingprocess of the silicon nitride film, etching is controlled accurately byusing the monitor and a thickness of the silicon nitride film to beetched is 100 to 2000 Å. Therefore, even though overetching isperformed, an etching depth is very shallower than that of the gateelectrode and the gate insulating film, so that no influence is providedsubstantially with the gate electrode and the gate insulating film.Further, since the anodic oxide film is formed under the silicon nitridefilm, the gate electrode is protected.

As described above, a method for etching a silicon nitride film iseffective in a case wherein a material of a gate insulating film is thesame material as an interlayer insulator and the material is not asilicon nitride. That is, when the interlayer insulator is formed afteretching the silicon nitride film, etching can be performed at one stagein formation of contact holes.

In the above stages, there is several cases for doping to form sourceand drain regions of a TFT. When only N-channel type TFT is formed on asubstrate, an N-type impurity having a relatively high concentration maybe introduced into a semiconductor layer using the gate electrode as amask in a self-alignment in a process between the first and secondstages. When an anodic oxide film is formed on side surfaces of the gateelectrode, so-called offset gate type TFT in which the source and drainregions are spaced apart from the gate electrode by a thickness of theanodic oxide film is obtained. As described below, a normal TFT includessuch TFT.

When an N-channel type TFT having a low concentration drain (lightlydoped drain, LDD), an LDD type TFT is formed, after an impurity having arelatively low concentration is introduced into a semiconductor layer ina process between the first and second stages, an N-type impurity havinga higher concentration is introduced in the semiconductor in aself-alignment using a gate electrode and side walls as masks. A widthof an LDD region is approximately equal to that of the side walls. Whenonly P-channel type TFT is formed, the above process may be performed.

When an offset type TFT is formed, an impurity may be introduced into asemiconductor layer using a gate electrode and side walls as masks in aself-alignment in a process between the second and third stages. In thisstate, a width of an offset is approximately equal to that of the sidewalls. In a TFT having such structure, a width of a substantiallyintrinsic region which becomes a channel forming region is approximatelyequal to summation of a width of the gate electrode and widths of sidewalls formed on the side surfaces of the gate electrode.

Also, a complementary type circuit (CMOS circuit) having N-channel typeand P-channel type TFTs can be formed by the above process. When bothN-channel type and P-channel type TFTs are constructed by using a normalTFT or an LDD type TFT, an impurity introduction for forming only one ofN-channel type and P-channel type TFTs may be used with respect to anN-type impurity and a P-type impurity.

When an N-channel type TFT necessary to prevent a hot carrier is formedas an LDD type TFT and a P-channel type TFT unnecessary to prevent a hotcarrier is formed as a normal TFT, a special impurity introductionprocess is performed. In this process, an N-type impurity having arelatively low concentration is introduced into a semiconductor layer ina process between the first and second stages. This is the firstimpurity introduction. In this state, an N-type impurity may beintroduced in a semiconductor layer of the P-channel type TFT.

Further, using the semiconductor layer of the N-channel type TFT as amask, a P-type impurity having a high concentration is introduced intoonly the semiconductor layer of the P-channel type TFT. This is thesecond impurity introduction. Even though the N-type impurity isincluded in the semiconductor layer of the P-channel type TFT by theabove N-type impurity introduction, since the P-type impurity having ahigher concentration is introduced by the P-type impurity introduction,a conductivity type of a semiconductor is a P-type. A concentration ofthe impurity introduced by the second impurity introduction is higherthan that of the impurity introduced by the first impurity introduction,by preferably 1 to 3 orders (digits).

Finally, in order to form the source and drain regions of the N-channeltype TFT, an N-type impurity having a relatively high concentration isintroduced in a process between the second and third stages. This is thethird impurity introduction. In this state, the impurity introductionmay be performed using a mask in order not to introduce the N-typeimpurity into the P-channel type TFT, or a mask may be not used. Whenthe mask is used, it is required that a concentration of the N-typeimpurity to be introduced is lower than that of a P-type impurityintroduced by the second impurity introduction, and the concentration ofthe N-type impurity is preferably {fraction (1/10)} to ⅔ of that of theP-type impurity. As a result, the N-type impurity is also introducedinto the P-channel type TFT. However, since the impurity concentrationis lower than that of the P-type impurity, a P-type is maintained.

In the present invention, step coverage of an interlayer insulator in anoverlap portion of gate electrode arrangements is improved by sidewalls, so that the frequency of disconnection of the second layerelectrode arrangement can be decreased. Also, an LDD structure and anoffset region can be obtained using the side walls.

In the present invention, a silicon nitride film is important. In thesecond stage, anisotropy etching is performed to form side walls.However, since it is difficult to control a plasma in an insulatingsurface, variations of etching (depth) within a substrate produce. Sincean etching depth is ⅓ to 2 times of a height (thickness) of a gateelectrode/arrangement, the variations are influenced largely. If thesilicon nitride film is not formed on an upper surface of a gateelectrode, the gate electrode and the gate insulating film may be etchedlargely (deeply) in a portion on the same substrate in a side walletching process. On the other hand, if the silicon nitride film isformed in the side wall etching process, etching is stopped, so that thegate electrode and the gate insulating film are protected. After that,when the silicon nitride film is removed by dry etching, an etchingdepth of the silicon nitride film is extremely smaller (shallower) thatof the side walls, so that gate electrode and the gate insulating filmmay be overetched. However, influence is not large. Also, even thoughoveretching is performed, the gate electrode is protected completely bythe anodic oxide film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F show a forming process of a TFT circuit according to afirst embodiment of the present invention;

FIGS. 2A and 2B show a forming process of a TFT circuit according to asecond embodiment;

FIGS. 3A and 3B show a forming process of a TFT circuit according to athird embodiment;

FIG. 4 shows a conventional forming process of a TFT circuit;

FIG. 5 shows a cross section view of a TFT circuit according to a fourthembodiment;

FIG. 6 shows a block diagram of the TFT circuit according to the fourthembodiment;

FIGS. 7A to 7F show a forming process of a TFT circuit according to afifth embodiment;

FIGS. 8A to 8G show a forming process of a TFT circuit according to asixth embodiment;

FIGS. 9A and 9F show a forming process of a TFT circuit according to aseventh embodiment;

FIGS. 10A and 10F show a forming process of a TFT circuit according toan eighth embodiment;

FIGS. 11A to 11E show a cross section view of a TFT circuit according toa ninth embodiment;

FIGS. 12A to 12F show a forming process of a TFT circuit according to atenth embodiment;

FIGS. 13A to 13F show a forming process of a TFT circuit according to aneleventh embodiment;

FIGS. 14A to 14F show a forming process of a TFT circuit according to atwelfth embodiment; and

FIGS. 15A to 15G show a forming process of a TFT circuit according to athirteenth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[Embodiment 1]

FIGS. 1A to 1F show a first embodiment. A silicon oxide film having athickness of 1000 to 1500 Å, for example, 2000 Å, is formed as a baseoxide film 102 on a substrate (Corning 7059, a size of 300 mm×400 mm or100 mm×100 mm) 101 by sputtering in an oxygen atmosphere. To improvemass productivity, the oxide film may be formed by decomposing anddepositing a TEOS using plasma CVD. Such formed silicon oxide film maybe annealed at 400 to 650° C.

An amorphous silicon film having a thickness of 300 to 5000 Å,preferably 400 to 1000 Å, for example, 500 Å is deposited by plasma CVDand low pressure CVD (LPCVD), and then is placed in a reduced atmosphereat 550 to 600° C. for 8 to 24 hours, to crystallize it. In this state,crystallization may be promoted by adding a metal element such as nickelwhich promotes crystallization, at an extremely small quantity. Thisprocess may be performed by laser irradiation. The crystallized siliconfilm is etched to form an island region 103. Further, a silicon oxidefilm 104 having a thickness of 700 to 1500 Å, for example, 1200 Å isformed on the silicon film by plasma CVD.

An aluminum (including Si of 1 weight % or Sc (scandium) of 0.1 to 0.3weight %) film having a thickness of 1000 Å to 3 μm, for example, 5000Å, is formed by sputtering and then etched to form a gate electrode 105and a gate electrode arrangement (wiring) 106. (FIG. 1A)

Anodization is performed by supplying a current to the gate electrode105 and the gate electrode arrangement 106 in an electrolytic solution,so that anodic oxides 107 and 108 each having a thickness of 500 to 2500Å, for example, 2000 Å, are formed. The electrolytic solution isobtained by diluting an ethylene glycol with L-tartaric acid at aconcentration of 5% and by adjusting it at 7.0±0.2 pH using ammonia. Thesubstrate is immersed into the electrolytic solution. A positive (+)side terminal of a constant current source is connected with the gateelectrode arrangement on the substrate and a negative (−) side terminalof the constant current source is connected with a platinum electrode,and then a voltage is applied in a constant current state. Oxidizationis continued until the applied voltage reaches 150 V. Further,oxidization is continued until a current reaches 0.1 mA or less whileapplying 150 V in a constant voltage state with 20 mA. As a result, analuminum oxide film having a thickness of 2000 Å is obtained.

By ion doping, an impurity (phosphorus, P) is implanted into the islandsilicon film 103 using a gate electrode portion (a gate electrode and asurrounding anodic oxide film) as a mask in a self-alignment, to formlow concentration impurity regions (LDDs) 109 as shown in FIG. 1B. Adose is 1×10¹³ to 5×10¹⁴ atoms/cm², for example, 5×10¹³ atoms/cm². Anaccelerating voltage is 10 to 90 kV, for example, 80 kV. (FIG. 1B)

By plasma CVD, a silicon oxide film 110 is deposited. Raw gases are TEOSand oxygen, or monosilane and nitrous oxide. A suitable thickness of thesilicon oxide film 110 is changed by a height (thickness) of a gateelectrode arrangement. When a height of the gate electrode/arrangementincluding an anodic oxide film is about 6000 Å, the suitable thicknessis preferably 2000 Å to 1.2 μm which is ⅓ to 2 times the height of thegate electrode/arrangement, 6000 Å in the embodiment. In this filmformation, it is necessary to obtain not only uniformity of a filmthickness in an even portion but also superior step coverage. As aresult, a thickness of a silicon oxide film formed on a side surfaceportion of the gate electrode/arrangement is thick by a portion as shownin a dotted line of FIG. 1C. (FIG. 1C)

By anisotropy etching using a well known reactive ion etching (RIE), thesilicon oxide film 110 is etched. This etching is completed when etchingreaches the gate insulating film 105. The etching stop timing can becontrolled by lowering an etching rate of the gate insulating film 105than that of the silicon oxide film 110. By the above process,insulators (side walls) 111 and 112 each having a approximatelyrectangular shape remain in side surfaces of the gateelectrode/arrangement. (FIG. 1D)

By ion doping, phosphorous (P) is introduced. It is preferred that adose is larger 1 to 3 orders (figures) than that in the process of FIG.1B. In the embodiment, the dose is 40 times the dose of first phosphorusdoping, that is, 2×10¹⁵ atoms/cm². An accelerating voltage is 80 kV. Asa result, regions (source/drain) 114 into which phosphorus is introducedat a high concentration are formed. Also, low concentration regions(LDDs) 113 remain under the side walls. (FIG. 1E)

A KrF excimer laser (wavelength of 248 nm and pulse width of 20 ns) isirradiated to activate the doped impurity. A suitable energy density ofa laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm². In theembodiment, since aluminum is used in a gate electrode/arrangement,there is a problem in heat resistance. Instead of laser irradiation,thermal annealing may be performed.

A silicon oxide film having a thickness of 5000 Å is formed as aninterlayer insulator 115 on a whole surface by CVD. Contact holes areformed in source and drain regions of a TFT, and then an aluminumarrangement 116 and an aluminum electrode 117 in the second layer areformed. A thickness of the aluminum arrangement is approximately equalto the gate electrode/arrangement, and 4000 to 6000 Å.

By the above process, an N-channel type TFT having LDDs are completed.In order to activate impurity regions, hydrogen annealing may be furtherperformed at 200 to 400° C. Since a step in an overlap portion which thesecond layer arrangement 117 overlaps the gate arrangement 106 has asmall sloop by the side walls 112, although a thickness of the secondlayer arrangement is approximately (nearly) equal to a gateelectrode/arrangement, disconnection in a step is not almost observed.(FIG. 1F)

With respect to a thickness of the second layer arrangement, when athickness of a gate electrode/arrangement is x (Å) and a thickness ofthe second layer arrangement is y (Å), if y≧x−1000 (Å), a remarkablydisconnection is not observed in an experiment by the inventors. Thesmaller value y is preferred. In particular, in a circuit which it isnecessary to even (smooth) a surface of a substrate, such as an activematrix circuit of a liquid crystal display device, it is desired thatx−1000 (Å)≦y≦x+1000 (Å).

[Embodiment 2]

FIGS. 2A to 2F show a second embodiment. The embodiment relates to anomolithic type active matrix circuit in which an active matrix circuitand a driver circuit are formed simultaneously on the same substrate. Inthe embodiment, a switching element of an active matrix circuit has aP-channel type TFT, and a driver circuit has a complementary typecircuit constructed by N-channel type and P-channel type TFTs. Infigures, an N-channel type TFT used in a driver circuit is shown in aleft side and a P-channel type TFT used in the driver circuit and anactive matrix circuit is shown in a right side. A P-channel type TFT isused as a switching element of an active matrix circuit because a leakcurrent (off current) is small.

As similar to Embodiment 1, a silicon oxide film is formed as a baseoxide film 202 on a substrate (Corning 7059) 201. Island siliconsemiconductor regions are deposited and then silicon oxide film 203 isformed as a gate insulating film on the silicon regions. An aluminumfilm having a thickness of 5000 Å is formed to obtain gate electrodes204 and 205. After that, as similar to Embodiment 1, anodization isperformed to form anodic oxides each having a thickness of 2000 Å aroundeach gate electrode (in upper and side surfaces of each gate electrode).By ion doping, phosphorus (P) is implanted using a gate electrodeportion as a mask, to form low concentration N-type impurity regions 206and 207. A dose is 1×10¹³ atoms/cm².

A KrF excimer laser (wavelength of 248 nm and pulse width of 20 ns) isirradiated to activate the doped impurity. A suitable energy density ofa laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm2. (FIG. 2A)

After an N-channel type TFT is masked by a photoresist 208, boron (B)having a high concentration is doped by ion doping. A dose is 5×10¹⁵atoms/cm². An accelerating voltage is 65 kV. As a result, the impurityregions 207 which becomes a weak N-type by a previous phosphorous dopingbecomes P-type impurity regions 209 by inverting into an intense P-type.After that, the impurity is activated by laser irradiation again. (FIG.2B) In the embodiment, a partial selective doping with a highconcentration boron is performed after a whole doping with a lowconcentration phosphorus. However, a whole doping with a lowconcentration phosphorus may be performed after a partial selectivedoping with a high concentration boron.

After the photoresist 208 as a mask is removed, a silicon oxide film 210having a thickness of 4000 to 8000 Å is deposited by plasma CVD. (FIG.2C)

As similar to Embodiment 1, by anisotropy etching, side walls 211 and212 of a silicon oxide are formed on side surfaces of the gateelectrodes. (FIG. 2D)

By ion doping, phosphorous (P) is introduced again. It is preferred thata dose is larger 1 to 3 orders (figures) than that in the process ofFIG. 2A and {fraction (1/10)} to ⅔ of the dose in the process of FIG.2B. In the embodiment, the dose is 200 times the dose of firstphosphorus doping, that is, 2×10¹⁵ atoms/cm². This dose is 40% of thedose of boron in the process of FIG. 2B. An accelerating voltage is 80kV. As a result, regions (source/drain) 213 into which phosphorus isintroduced at a high concentration are formed. Also, low concentrationregions (LDDs) 214 remain under the side walls. (FIG. 2E)

A KrF excimer laser (wavelength of 248 nm and pulse width of 20 ns) isirradiated to activate the doped impurity. A suitable energy density ofa laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm².

Although phosphorous is also doped in a p-channel type TFT (right sidein a figure), since a concentration of previously doped boron is 2.5times that of phosphorus, a P-type is maintained. Although it appearsthat P-type regions of the P-channel type TFT include regions 216 formedunder the side walls and regions 215 formed outside the regions 216 (inpositions opposite to a channel forming regions), a remarkablydifference between them on electrical characteristics does not appear.(FIG. 2E)

As shown in FIG. 2F, a silicon oxide film having a thickness of 3000 Åis formed as an interlayer insulator 217 on a whole surface by CVD.Contact holes are formed in source and drain regions of a TFT, and thenaluminum electrode arrangements 218, 219, 220 and 221 are formed. By theabove process, a semiconductor integrated circuit using an N-channeltype TFT having LDDs are completed.

Although not shown in figures, an interlayer insulator is not so thickin an overlap portion in which the second layer arrangement overlaps agate electrode/arrangement. However, as similar to Embodiment 1,disconnection is not almost appeared.

In order to prevent deterioration of a TFT by a hot carrier, in theembodiment, an N-channel type TFT has LDD structures. However, LDDregions correspond to parasitic resistors serial-connected to source anddrain regions, an operation speed of the TFT is reduced. Therefore, itis desired that a TFT does not include LDD regions in a P-channel typeTFT which a mobility is small and deterioration by a hot carrier isless.

In the embodiment, when a doping process is performed, the dopedimpurity is activated by laser irradiation. However, after all dopingprocesses are completed and immediately before an interlayer insulatoris formed, doping processes may be performed.

[Embodiment 3]

FIGS. 3A and 3B show a third embodiment. The embodiment shows severaletchings for forming side walls in Embodiment 1. In FIG. 3A, a TFTregion 301 and a gate electrode arrangement 302 are shown. The formingprocess is the same as Embodiment 1 with FIGS. 1A to 1F.

In the embodiment, since etching with overetching is performed in ananisotropy etching process for forming side walls 304, the side wallsare positioned somewhat under an upper surface of a gateelectrode/arrangement. Also, etching is performed until it reaches agate insulating film 303.

In the embodiment, an etching rate of a material constructing the sidewalls is twice that of the gate insulating film 303. Therefore, eventhough the same etching condition is set, a depth which the gateinsulating film is etched is a half that of the side walls. A thicknessof the gate insulating film becomes a half of an original thickness byetching. On the other hand, thicknesses of the side walls 304 and angate insulating film 303′ formed under the a gate electrode/arrangementis the same as an original thickness. Also, since the gateelectrode/arrangement is covered with an anodic oxide, it is not almostdamaged in an anisotropy etching for forming side walls.

In this state, an interlayer insulator 305 is forme on a whole surface.Though the side walls 304 are formed in a lower position than Embodiment1, since a step around the vicinity of the gate electrode/arrangementhas a gently slope, in comparison with a conventional case, theinterlayer insulator covers an overlap portion 308 of a gateelectrode/arrangement sufficiently. After that, the second layerarrangements 306 and 307 are formed. However, since undulation of theinterlayer insulator 305 in the overlap portion 308, disconnection inthe overlap portion 308 is not produced.

FIG. 3B shows a case wherein an etching rate of a material constructingside walls 354 is equal to that of a gate insulating film 353.Therefore, the gate insulating film and the side walls are etched in thesame etching condition. In the embodiment, the gate insulating film isetched completely, so that an active layer of a TFT is exposed. In thisstate, undulation of an interlayer insulator 355 in an overlap portion,disconnection of second layer arrangements 356 and 357 in the overlapportion is not produced.

As shown in FIG. 3A, it is difficult to remain (etch) a gate insulatingfilm having a half of an original thickness. Therefore, As shown inFIGS. 1F or 3B, it is easy that a gate insulating film is not etched orthe gate insulating film is etched completely.

[Embodiment 4]

FIG. 6 shows a block diagram of a liquid crystal display device in whichan active matrix circuit, a peripheral driver circuit, a circuit such asa central processing unit (CPU) and the like are formed on the sameglass substrate. All TFTs constructing these circuits are formed on thesame substrate 601. In FIG. 6, a liquid crystal display device includesan active matrix circuit 602, an input port 610, a CPU 611, a correctionmemory 612, a memory 613, an X-Y divider 614, a Y-decoder/driver 615, anX-decoder/driver 616. The active matrix circuit 602 has a TFT 603arranged in one pixel, a pixel electrode 604 having a liquid crystal andan auxiliary capacitor 605.

The input port 610 receives a signal output from an external such as acomputer system, and converts the received signal into an image signal.The correction memory 612 is used to correct an input signal inaccordance with characteristics of an active matrix panel and isinherent to this panel. In particular, the correction memory 612 is annon-volatile memory and stores correction information inherent to eachpixel. If a pixel has a point defect, correction signals are supplied topixels around the pixel having a point defect, in order to cover a pointdefect and not to highlight a defect. If a pixel is darker thansurrounding pixels, a signal having a higher level is supplied to thepixel, to coincide with brightness of the surrounding pixels.

The CPU 611 and the memory 613 each has the same function as acommonly-used computer. In particular, the memory 613 is an image memoryfor storing image data corresponding to each pixel, as a random accessmemory (RAM). A backlight unit (not shown) for irradiating a substratewith a light from the rear side can be controlled in accordance withimage information.

FIG. 5 shows a cross section of such circuit. The circuit includes anactive matrix circuit (pixel circuit) region and a region which has aperipheral driver circuit, a CPU, a memory and the like, other than theactive matrix circuit region. In the embodiment, a complementary typecircuit which is constructed by an N-channel type TFT 515 and aP-channel type TFT 516 is used in the region other than the activematrix circuit region. A forming process is the same as Embodiment 2with FIGS. 2A to 2F. In the active matrix circuit region, a P-channeltype TFT 511 which is connected with a pixel electrode 512 is used. TheTFT 511 and the TFT 516 are formed simultaneously.

[Embodiment 5]

FIG. 7 shows a fifth embodiment. In the embodiment, as similar toEmbodiment 2, an N-channel type TFT having an LDD and a normal P-channeltype TFT are formed on the same substrate. In FIG. 7, an N-channel typeTFT is shown in a left side, a P-channel type TFT is shown in a rightside.

A silicon oxide film is formed as a base oxide film 702 on a substrate(Corning 7059) 701. Island silicon semiconductor regions are formed andthen a silicon oxide film 703 is formed as a gate insulating film on thesilicon regions. An aluminum film (a thickness of 5000 Å) which asurface is covered with an anodic oxide is formed to obtain gateelectrodes 704 and 705. The gate insulating film with respect to anN-channel type TFT is selectively etched using the gate electrode 704 asa mask, to expose the semiconductor regions. By ion doping, phosphorusis implanted using a gate electrode portion as a mask, to form a lowconcentration N-type impurity region 706. A dose is 1×10¹³ atoms/cm². Anaccelerating voltage is 20 kV. In this process, since the acceleratingvoltage is low, phosphorus is not implanted into an island region 707 ofa P-channel type TFT covered with the gate insulating film 703. (FIG.7A)

After the N-channel type TFT is masked by a photoresist 708, boron (B)having a high concentration is doped by ion doping. A dose is 5×10¹⁴atoms/cm². An accelerating voltage is 65 kV. As a result, a P-typeimpurity regions 709 is formed in the island region 707. (FIG. 7B)

In the embodiment, a partial selective doping with a high concentrationboron is performed after a whole doping with a low concentrationphosphorus. However, a whole doping with a low concentration phosphorusmay be performed after a partial selective doping with a highconcentration boron.

After the photoresist 708 as a mask is removed, a silicon oxide film 710having a thickness of 4000 to 8000 Å is deposited by plasma CVD. (FIG.7C)

As similar to Embodiment 2, by anisotropy etching, side walls 711 and712 of a silicon oxide are formed on side surfaces of the gateelectrodes. (FIG. 7D)

By ion doping, phosphorous is introduced again. It is preferred that adose is larger 1 to 3 orders (figures) than that in the process of FIG.7A. In the embodiment, the dose is 200 times the dose of firstphosphorus doping, that is, 2×10¹⁵ atoms/cm². An accelerating voltage is20 kV. As a result, regions (source/drain) 713 into which phosphorus isintroduced at a high concentration are formed. Also, low concentrationregions (LDDs) 714 remain under the side walls.

On the other hand, in the P-channel type TFT, since the gate insulatingfilm is formed, phosphorus ion is not implanted. In Embodiment 2, sincephosphorus and boron are implanted at a high concentration, a dose rangeis limited. In the embodiment, a dose range is not limited. However, itis desired that a dose of phosphorus is low and a dose of boron is high.(FIG. 7E)

After doping process, a KrF excimer laser (wavelength of 248 nm andpulse width of 20 ns) is irradiated to activate the doped impurity. Asuitable energy density of a laser is 200 to 400 mJ/cm², preferably 250to 300 mJ/cm².

As shown in FIG. 7F, a silicon oxide film having a thickness of 5000 Åis formed as an interlayer insulator 715 on a whole surface by CVD.Contact holes are formed in source and drain regions of a TFT, and thenaluminum electrode arrangements 716, 717, 718 and 719 are formed. By theabove process, a semiconductor integrated circuit using an N-channeltype TFT having LDDs are completed.

In the embodiment, in comparison with Embodiment 2, a photolithographyprocess and an etching process are further performed to remove the gateoxide film of the N-channel type TFT. However, an N-type impurity is notintroduced substantially into the P-channel type TFT, it is merit that adose of N type and P-type impurities is can be changed easily.

Also, since phosphorus implanted into the vicinity of a surface of thegate insulating film 703 in the P-channel type TFT is used to form aglass containing phosphorus by a later laser irradiating process, it iseffective in preventing entering of an active ion such as sodium.

[Embodiment 6]

FIGS. 8A to 2G show a sixth embodiment. The embodiment relates to amethod for forming an active matrix type liquid crystal display device.In figures, an N-channel type TFT having an LDD (center portion) and anormal P-channel type TFT (left side) are logical circuits used in adriver circuit and the like, and a P-channel type TFT having an offset(right side) is a switching transistor used in an active matrix array.

A silicon oxide film is formed as a base oxide film on a substrate(Corning 7059). Island silicon semiconductor regions (an island region801 for a peripheral circuit and an island region 802 for an activematrix circuit) are deposited and then silicon oxide film 803 is formedas a gate insulating film on the silicon regions. An aluminum film (athickness of 5000 Å) which a surface is covered with an anodic oxide isformed to obtain gate electrodes 804 and 805 for a peripheral circuitand a gate electrode 806 for an active matrix circuit.

The gate insulating film of the P-channel type TFT for a peripheralcircuit and an active matrix circuit is selectively removed using thegate electrodes 804 and 806 as masks to expose the semiconductorregions. An active matrix circuit region is masked by a photoresist 807and then boron is implanted using a gate electrode portion as a mask byion doping, to form high concentration P-type impurity regions 808. Adose is 1×10¹⁵ atoms/cm², and an accelerating voltage is 20 keV. In thisdoping process, since an accelerating voltage is low, boron is not dopedinto the N-channel type TFT covered with the gate insulating film 803.(FIG. 8A)

After that, phosphorus is doped at a low concentration by ion doping. Adose is 1×10¹³ atoms/cm², and an accelerating voltage is 80 kV. As aresult, low concentration N-type impurity regions 809 are formed in theN-channel type TFT. (FIG. 8B)

In FIG. 8B, doping is performed after the photoresist 806 as a mask isremoved. Doping may be performed without removing the photoresist. Sincean accelerating voltage with respect to phosphorus is high, when thedoping is performed without removing the photoresist, phosphorus is notimplanted into the active matrix circuit region. Therefore, an idealP-channel type TFT having an offset is obtained. However, since thephotoresist is ashed by doping, removing of the photoresist takes timein a case.

When the photoresist is removed, since an accelerating voltage withrespect to phosphorus is high, a concentration peak of phosphorusproduces under the island semiconductor regions. However, it cannot beassured that phosphorus is not doped completely into the islandsemiconductor regions, so that phosphorus having an extremely smallquantity is introduced into the island semiconductor regions. Eventhough phosphorus is doped, a concentration of phosphorus is less. Thisis preferred in a TFT for an active matrix circuit which has P⁺ (source)n⁻ (channel)/n⁻/P⁺ (drain) and is required to decrease a leak current.

After that, a silicon oxide film having a thickness of 4000 to 8000 Å isdeposited by plasma CVD. Further, as similar to Embodiment 2, byanisotropy etching, side walls 810, 811 and 812 of a silicon oxide areformed on side surfaces of the gate electrodes. (FIG. 8C)

By ion doping, boron is introduced again. It is desired that a dose isapproximately equal to that of the process of FIG. 8A. In theembodiment, the dose is 1×10¹⁵ atoms/cm², and an accelerating voltage is20 keV. Since an accelerating voltage is low, boron is not doped intothe N-channel type TFT on which the gate insulating film 803 is formed,so that boron is mainly doped into source and drain regions of theP-channel type TFTs for a peripheral circuit and an active matrixcircuit. As a result, source and drain regions 813 of a TFT for anactive matrix circuit are formed. This TFT has an offset structure inwhich the gate electrode is spaced apart from the source and drainregions. (FIG. 8D)

Next, phosphorous is introduced. It is preferred that a dose is larger 1to 3 orders (figures) than that in the first phosphorus doping processof FIG. 8B. In the embodiment, the dose is 50 times the dose of thefirst phosphorus doping, that is, 5×10¹⁴ atoms/cm². An acceleratingvoltage is 80 kV. As a result, regions (source/drain) 814 into whichphosphorus is introduced at a high concentration are formed. Also, lowconcentration regions (LDDs) 815 remain under the side walls. On theother hand, since phosphorus ion is almost implanted into a base film inthe P-channel type TFT, phosphorus does not influence a conductivitytype. (FIG. 8E)

After the doping process, a KrF excimer laser (wavelength of 248 nm andpulse width of 20 ns) is irradiated to activate the doped impurity. Asuitable energy density of a laser is 200 to 400 mJ/cm², preferably 250to 300 mJ/cm².

A silicon nitride film having a thickness of 5000 Å is formed as a firstinterlayer insulator 816 on a whole surface by CVD. Contact holes areformed in source and drain regions of a TFT, and then aluminum electrodearrangements 817, 818, 819 and 820 are formed. By the above process, aperipheral circuit region is formed. (FIG. 8F)

Further, a silicon oxide film having a thickness of 3000 Å is formed asa second interlayer insulator 821 by CVD. Contact holes are formed byetching the silicon oxide film, and then a pixel electrode 822 is formedusing a transparent conductive film in a TFT for an active matrixcircuit. By the above process, an active matrix type liquid crystaldisplay substrate is produced. (FIG. 8G)

[Embodiment 7]

FIGS. 9A to 9F show a seventh embodiment. A silicon oxide film having athickness of 1000 to 1500 Å, for example, 2000 Å, is formed as a baseoxide film 1102 on a substrate (Corning 7059, a size of 300 mm×400 mm or100 mm×100 mm) 1101 by sputtering in an oxygen atmosphere. To improvemass productivity, the oxide film may be formed by decomposing anddepositing a TEOS using plasma CVD. Such formed silicon oxide film maybe annealed at 400 to 650° C.

An amorphous silicon film having a thickness of 300 to 5000 Å,preferably 400 to 1000 Å, for example, 500 Å is deposited by plasma CVDand LPCVD, and then is placed in a reduced atmosphere at 550 to 600° C.for 8 to 24 hours, to crystallize it. In this state, crystallization maybe promoted by adding a metal element such as nickel which promotescrystallization, at an extremely small quantity. This process may beperformed by laser irradiation. The crystallized silicon film is etchedto form an island region 1103. Further, a silicon oxide film 1104 havinga thickness of 700 to 1500 Å, for example, 1200 Å, is formed as a gateinsulating film on the silicon film by plasma CVD.

An aluminum (including Sc (scandium) of 0.1 to 0.3 weight %) film havinga thickness of 1000 Å to 3 μm, for example, 5000 Å, is formed bysputtering and then etched to form a gate electrode 1105 and a gateelectrode arrangement (wiring) 1106. (FIG. 9A) Anodization is performedby supplying a current to the gate electrode 1105 and the gate electrodearrangement 1106 in an electrolytic solution, so that anodic oxides 1107each having a thickness of 500 to 2500 Å, for example, 2000 Å, areformed. The electrolytic solution is obtained by diluting an ethyleneglycol with L-tartaric acid at a concentration of 5% and by adjusting itat 7.0±0.2 pH using ammonia. The substrate is immersed into theelectrolytic solution. A positive (+) side terminal of a constantcurrent source is connected with the gate electrode/arrangement on thesubstrate and a negative (−) side terminal of the constant currentsource is connected with a platinum electrode, and then a voltage isapplied in a constant current state with 20 mA. Oxidization is continueduntil the applied voltage reaches 150 V. Further, oxidization iscontinued until a current reaches 0.1 mA or less while applying 150 V ina constant voltage state. As a result, an aluminum oxide film having athickness of 2000 Å is obtained.

By plasma CVD using a mixed gas (NH₃/SiH₄/H₂), a silicon nitride film1108 having a thickness of 100 to 2000 Å, preferably, 200 to 1000 Å, forexample, 500 Å, is formed. Another CVD may be used in the filmformation. However, it is desired that step coverage of a gate electrodeis superior.

By ion doping, an impurity (phosphorus, P) is implanted into the islandsilicon film 1103 using a gate electrode portion as a mask in aself-alignment, to form low concentration impurity regions (LDDs) 1109as shown in FIG. 9B. A dose is 1×10¹³ to 5×10¹⁴ atoms/cm², for example,5×10¹³ atoms/cm². An accelerating voltage is 10 to 90 kV, for example,80 kV. (FIG. 9B)

By plasma CVD, a silicon oxide film 1110 is deposited. Raw gases areTEOS and oxygen, or monosilane and nitrous oxide. A suitable thicknessof the silicon oxide film 1110 is changed by a height (thickness) of agate electrode/arrangement. When a height (thickness) of the gateelectrode/arrangement including a silicon nitride film is about 5000 Å,the suitable thickness is preferably 2000 Å to 1.2 μm which is ⅓ to 2times the height of the gate electrode/arrangement, 6000 Å in theembodiment. In this film formation, it is necessary to obtain not onlyuniformity of a film thickness in an even portion but also superior stepcoverage. As a result, a thickness of a silicon oxide film formed on aside surface portion of the gate electrode/arrangement is thick by aportion as shown in a dotted line of FIG. 9C. (FIG. 9C)

By anisotropy etching using a well known reactive ion etching (RIE), thesilicon oxide film 1110 is etched. This etching is completed whenetching reaches the silicon nitride film 1108. The silicon nitride filmis not etched easily by anisotropy etching using the RIE, so that thegate insulating film 1104 is not etched. By the above process,insulators (side walls) 1111 and 1112 each having a substantiallyrectangular shape remain in side surfaces of the gateelectrode/arrangement. (FIG. 9D)

By ion doping, phosphorous (P) is introduced again. It is preferred thata dose is larger 1 to 3 orders (figures) than that in the process ofFIG. 9B. In the embodiment, the dose is 40 times the dose of firstphosphorus doping, that is, 2×10¹⁵ atoms/cm². An accelerating voltage is80 kV. As a result, regions (source/drain) 1114 into which phosphorus isintroduced at a high concentration are formed. Also, low concentrationregions (LDDs) 1113 remain under the side walls. (FIG. 9E)

A KrF excimer laser (wavelength of 248 nm and pulse width of 20 ns) isirradiated to activate the doped impurity. A suitable energy density ofa laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm². In theembodiment, since aluminum is used in a gate electrode/arrangement,there is a problem in heat resistance, so that it is difficult to usealuminum. However, when a gate electrode is formed using a materialhaving a high heat resistance, instead of laser irradiation, thermalannealing may be performed.

A silicon oxide film having a thickness of 5000 Å is formed as aninterlayer insulator 1115 on a whole surface by CVD. Contact holes areformed in source and drain regions of a TFT, and then an aluminumarrangement 1116 and an aluminum electrode 1117 in the second layer areformed. A thickness of the aluminum arrangement is approximately equalto that of the gate electrode/arrangement, and 4000 to 6000 Å.

By the above process, an N-channel type TFT having LDDs is completed. Inorder to activate impurity regions, hydrogen annealing may be furtherperformed at 200 to 400° C. Since a step in an overlap portion which thesecond layer arrangement 1117 overlaps the gate arrangement 1106 has asmall sloop by the side walls 112, although a thickness of the secondlayer arrangement is approximately (nearly) equal to a gateelectrode/arrangement, disconnection in a step is not almost observed.(FIG. 9F)

With respect to a thickness of the second layer arrangement, when athickness of a gate electrode/arrangement is x (Å) and a thickness ofthe second layer arrangement is y (Å), if y≧x−1000 (Å) a remarkablydisconnection is not observed in an experiment by the inventors. Thesmaller value y is preferred. In particular, in a circuit which it isnecessary to even (smooth) a surface of a substrate, such as an activematrix circuit of a liquid crystal display device, it is desired thatx−1000 (Å)≦y≦x+1000 (Å).

[Embodiment 8]

FIGS. 10A to 10F show an eighth embodiment. The embodiment relates to anomolithic type active matrix circuit in which an active matrix circuitand a driver circuit are formed simultaneously on the same substrate. Inthe embodiment, a switching element of an active matrix circuit has aP-channel type TFT, and a driver circuit has a complementary typecircuit constructed by N-channel type and P-channel type TFTs. Infigures, an N-channel type TFT used in a driver circuit is shown in aleft side and a P-channel type TFT used in the driver circuit and anactive matrix circuit is shown in a right side. A P-channel type TFT isused as a switching element of an active matrix circuit because a leakcurrent (off current) is small.

As similar to Embodiment 7, a silicon oxide film is formed as a baseoxide film 1202 on a substrate (Corning 7059) 1201. Island siliconsemiconductor regions are formed and then silicon oxide film 1203 isformed as a gate insulating film on the silicon semiconductor regions.An aluminum film having a thickness of 5000 Å is formed to obtain gateelectrodes 1204 and 1205. After that, as similar to Embodiment 7,anodization is performed to form anodic oxides 1206 each having athickness of 2000 Å around each gate electrode (in upper and sidesurfaces of each gate electrode). A silicon nitride film 1207 having athickness of 100 to 2000 Å, for example, 1000 Å, is formed. By iondoping, phosphorus (P) is implanted using a gate electrode portion as amask, to form low concentration N-type impurity regions 1208 and 1209. Adose is 1×10¹³ atoms/cm².

A KrF excimer laser (wavelength of 248 nm and pulse width of 20 ns) isirradiated to activate the doped impurity. A suitable energy density ofa laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm². (FIG. 10A)

After an N-channel type TFT is masked by a photoresist 1210, boron (B)having a high concentration is doped by ion doping. A dose is 5×10¹⁵atoms/cm². An accelerating voltage is 65 kV. As a result, the impurityregions 1208 which becomes a weak N-type by a previous phosphorousdoping becomes P-type impurity regions 1211 by inverting into an intenseP-type. After that, the impurity is activated by laser irradiationagain. (FIG. 10B)

After the photoresist 1210 as a mask is removed, a silicon oxide film1212 having a thickness of 4000 to 8000 Å is deposited by plasma CVD.(FIG. 10C)

As similar to Embodiment 7, by anisotropy etching, side walls 1213 and1214 of a silicon oxide are formed on side surfaces of the gateelectrodes. (FIG. 10D)

By ion doping, phosphorous (P) is introduced again. It is preferred thata dose is larger 1 to 3 orders (figures) than that in the process ofFIG. 10A and {fraction (1/10)} to ⅔ of the dose in the process of FIG.10B. In the embodiment, the dose is 200 times the dose of firstphosphorus doping, that is, 2×10¹⁵ atoms/cm². This dose is 40% of thedose of boron in the process of FIG. 10B. An accelerating voltage is 80kV. As a result, regions (source/drain) 1215 into which phosphorus isintroduced at a high concentration are formed. Also, low concentrationregions (LDDs) 216 remain under the side walls. (FIG. 10E)

Further, a KrF excimer laser (wavelength of 248 nm and pulse width of 20ns) is irradiated to activate the doped impurity. A suitable energydensity of a laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm².

Although phosphorous is also doped in a p-channel type TFT (a right sidein a figure), since a concentration of previously doped boron is 2.5times that of phosphorus, a P-type is maintained. Although it appearsthat P-type regions of the P-channel type TFT include regions 1218formed under the side walls and regions 1217 formed outside the regions1218 (in positions opposite to a channel forming regions), a remarkablydifference between them on electrical characteristics does not appear.(FIG. 10E)

As shown in FIG. 10F, a silicon oxide film having a thickness of 3000 Åis formed as an interlayer insulator 1219 on a whole surface by CVD.Contact holes are formed in source and drain regions of a TFT, and thenaluminum electrode arrangements 1220, 1221, 1222 and 1223 are formed. Bythe above process, a semiconductor integrated circuit using an N-channeltype TFT having LDDs are completed.

Although not shown in figures, an interlayer insulator is not so thickin an overlap portion in which the second layer arrangement overlaps agate electrode/arrangement. However, as similar to Embodiment 7,disconnection is not almost appeared.

In order to prevent deterioration of a TFT by a hot carrier, in theembodiment, an N-channel type TFT has LDD structures. However, LDDregions correspond to parasitic resistors serial-connected to source anddrain regions, an operation speed of the TFT is reduced. Therefore, itis desired that a TFT does not include LDD regions in a P-channel typeTFT which a mobility is small and deterioration by a hot carrier isless.

In the embodiment, when a doping process is performed, the dopedimpurity is activated by laser irradiation. However, after all dopingprocesses are completed and immediately before an interlayer insulatoris formed, doping processes may be performed.

[Embodiment 9]

FIGS. 11A and 11E show a ninth embodiment. The embodiment relates to amethod for forming a TFT having an offset region using side walls.

A silicon oxide film having a thickness of 2000 Å is formed as a baseoxide film 1302 on a substrate 1301. An amorphous silicon film having athickness of, for example, 500 Å, is deposited by plasma CVD and LPCVD,and then is placed in a reduced atmosphere at 550 to 600° C. for 8 to 24hours, to crystallize it. The crystallized silicon film is etched toform an island region 1303. Further, a silicon oxide film 1304 having athickness of 1200 Å is formed on the silicon film by plasma CVD.

An aluminum. (including Si of 1 weight % or Sc (scandium) of 0.1 to 0.3weight %) film having a thickness of 5000 Å is formed by sputtering andthen etched to form a gate electrode 1305 and a gate electrodearrangement (wiring) 1306.

Anodic oxides 307 each having a thickness of 2000 Å are formed aroundthe gate electrode (in upper and side surfaces of the gate electrode) byanodization. (FIG. 11A)

Also, by plasma CVD using a mixed gas (NH₃/SiH₄/H₂), a silicon nitridefilm 1308 having a thickness of 200 to 1000 Å is formed.

By plasma CVD, a silicon oxide film 1309 is deposited. Raw gases areTEOS and oxygen, or monosilane and nitrous oxide. A suitable thicknessof the silicon oxide film 1309 is changed by a height (thickness) of agate electrode/arrangement. When a height (thickness) of the gateelectrode/arrangement including a silicon nitride film is about 6000 Å,the suitable thickness is preferably 2000 Å to 1.2 μm which is ⅓ to 2times the height of the gate electrode/arrangement, 6000 Å in theembodiment. In this film formation, it is necessary to obtain not onlyuniformity of a film thickness in an even portion but also superior stepcoverage. (FIG. 11B)

By anisotropy etching using a well known RIE, the silicon oxide film1309 is etched. This etching is completed when etching reaches thesilicon nitride film 1308. The silicon nitride film is not etched easilyby anisotropy etching using the RIE, so that the gate insulating film1304 is not etched. By the above process, insulators (side walls) 1310and 1311 each having a substantially rectangular shape remain in sidesurfaces of the gate electrode/arrangement. (FIG. 11C)

By ion doping, phosphorous (P) is introduced. A dose is 1×10¹⁴ to 5×10¹⁷atoms/cm², for example, 2×10¹⁵ atoms/cm². An accelerating voltage is 10to 90 kV, for example, 80 kV. As a result, regions (source/drain) 1312into which phosphorus is introduced are formed. Also, offset regionswhich phosphorus is not introduced are formed under the side walls.(FIG. 11D)

Further, a KrF excimer laser (wavelength of 248 nm and pulse width of 20ns) is irradiated to activate the doped impurity. A suitable energydensity of a laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm².

A silicon oxide film having a thickness of 5000 Å is formed as aninterlayer insulator 1313 on a whole surface by CVD. Contact holes areformed in source and drain regions of a TFT, and then an aluminumarrangement 1314 and an aluminum electrode 1315 in the second layer areformed. A thickness of the aluminum arrangement is approximately equalto that of the gate electrode/arrangement, and 4000 to 6000 Å.

By the above process, an N-channel type TFT having offset regions iscompleted. Since a step in an overlap portion which the second layerarrangement 1315 overlaps the gate electrode arrangement 1306 has asmall sloop by the side walls 1311, although a thickness of the secondlayer arrangement is approximately (nearly) equal to a gateelectrode/arrangement, disconnection in a step is not almost observed.(FIG. 11E)

[Embodiment 10]

FIGS. 12A to 12F show a tenth embodiment. In the embodiment, anN-channel type TFT having offsets and an N-channel type TFT having LDDsare formed on the same substrate.

As similar to Embodiment 7, a silicon oxide film is formed as a baseoxide film 1502 on a substrate (Corning 7059) 1501. Island siliconsemiconductor regions are formed and then a silicon oxide film (gateinsulating film) 1503 is formed on the silicon semiconductor regions.Gate electrodes 1504 and 1505 are formed using an aluminum film (athickness of 5000 Å). As similar to Embodiment 7, anodic oxides 506having a thickness 2000 Å are formed around the gate electrodes (onupper and side surfaces of the gate electrodes) by anodization. Further,by plasma CVD, a silicon nitride film 1507 having a thickness of 100 to2000 Å, for example, 1000 Å, is formed. (FIG. 12A) After a TFT havingoffset regions is masked by a photoresist 1508, by ion doping,phosphorus (P) is implanted into a TFT having LDDs using a gateelectrode portion as a mask, to form low concentration N-type impurityregions 1509 and 1209. A dose is 1×10¹³ atoms/cm².

Further, a KrF excimer laser (wavelength of 248 nm and pulse width of 20ns) is irradiated to activate the doped impurity. A suitable energydensity of a laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm².(FIG. 12B)

After the photoresist 1508 as a mask is removed,a silicon oxide film1510 having a thickness of 4000 to 8000 Å, for example, 6000 Å, isdeposited by plasma CVD. (FIG. 12C)

As similar to Embodiment 7, by anisotropy etching, the silicon oxidefilm 1510 is etched, so that insulators (side walls) 1511 and 1512 areformed on side surfaces of the gate electrode. (FIG. 12D)

By ion doping, phosphorous (P) is introduced again. It is preferred thata dose is larger 1 to 3 orders (figures) than that in the process ofFIG. 12B. In the embodiment, the dose is 200 times the dose of firstphosphorus doping, that is, 2×10¹⁵ atoms/cm². An accelerating voltage is80 kV. As a result, regions (source/drain) 1513 and 1514 into whichphosphorus is introduced at a high concentration are formed. Also, inthe process of FIG. 12B, offset regions remain under the side walls inthe masked TFT, and low concentration regions (LDDs) 1515 remain underthe side walls in the TFT into which phosphorus having a lowconcentration is doped.

Further, a KrF excimer laser (wavelength of 248 nm and pulse width of 20ns) is irradiated to activate the doped impurity. A suitable energydensity of a laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm².(FIG. 12E)

As shown in FIG. 12F, a silicon oxide film having a thickness of 3000 Åis formed as an interlayer insulator 1516 on a whole surface by CVD.Contact holes are formed in source and drain regions of a TFT, and thenaluminum electrode arrangements 1517, 1518, 1519 and 1520 are formed.

By the above process, a semiconductor integrated circuit which includesan N-channel type TFT having offsets and an N-channel type TFT havingLDDs is produced.

Although not shown in figures, an interlayer insulator is not so thickin an overlap portion in which the second layer arrangement overlaps agate electrode/arrangement. However, as similar to Embodiment 7,disconnection is not almost appeared.

In the embodiment, when a doping process is performed, the dopedimpurity is activated by laser irradiation. However, after all dopingprocesses are completed and immediately before an interlayer insulatoris formed, doping processes may be performed.

Also, the embodiment shows a case wherein only N-channel type TFTs areused. However, a CMOS circuit may be constructed by forming an N-channeltype TFT and a P-channel type TFT on the same substrate. For example, ina monolithic type active matrix circuit in which a peripheral circuitand an active matrix circuit are formed on the same substrate, a CMOScircuit which includes an N-channel LDD type TFT having a high speedoperation and a normal PMOS type TFT may be used. Also, in an activematrix circuit which decrease of a leak current is desired, an N-channeltype or P-channel type TFT having offsets may be used. In particular, aleak current decreases effectively by using the P-channel type TFThaving offsets. In a peripheral circuit, both an N-channel type TFT anda P-channel TFT may include LDDs.

[Embodiment 11]

FIGS. 13A to 13F show an eleventh embodiment. As similar to Embodiment7, a silicon oxide film having a thickness of 2000 Å is formed as a baseoxide film 1602 on a substrate (Corning 7059) 1601, and then an islandsilicon region having a thickness 500 Å is formed. Further, a siliconoxide film 1603 having a thickness of 1000 Å is formed as a gateinsulating film on the silicon region by plasma CVD.

Using an aluminum film having a thickness of 5000 Å, a gate electrode1604 and a gate electrode arrangement (wiring) 1605 are formed. Assimilar to Embodiment 7, anodization is performed to form anodic oxides1606 each having a thickness of 2000 Å around each gate electrode. Asilicon nitride film 1607 having a thickness of 100 to 2000 Å,preferably 200 to 1000 Å, for example, 500 Å, is formed.

By ion doping, an impurity (phosphorus, P) is implanted in the islandsilicon film using a gate electrode portion as a mask in aself-alignment, to form low concentration impurity regions (LDDS) 1608,as shown in FIG. 13A. A dose is 1×10¹³ to 5×10¹⁴ atoms/cm², for example,5×10¹³ atoms/cm². Accelerating voltage is 10 to 90 kV, for example, 80kV. (FIG. 13A)

By plasma CVD, a silicon oxide film 1609 having a thickness of 6000 Å isformed. In this film formation, it is necessary to obtain not onlyuniformity of a film thickness in an even portion but also superior stepcoverage. (FIG. 13B)

By anisotropy etching using CHF₃, the silicon oxide film 1609 is etched.Etching may be performed until is reaches the silicon nitride film 1607.However, as shown in FIG. 13C, etching may be stopped immediately beforeit reaches the silicon nitride film 1607 to remain the silicon oxidefilm 1609 slightly. By the above process, insulators (side walls) 1610and 1611 each having a substantially rectangular shape are formed onside surfaces of gate electrode/arrangements. (FIG. 13C)

Dry etching is performed using CH₄/O₂, to etch the silicon nitride filmand the silicon oxide film which remains slightly on the silicon nitridefilm. Since etching can be measured (monitored) by using an end pointmonitor (plasma monitor), overetching to a gate electrode and a gateinsulating film can be suppressed largely. (FIG. 13D)

By ion doping, phosphorous (P) is introduced again. It is preferred thata dose is larger 1 to 3 orders (figures) than that in the process ofFIG. 13A. In the embodiment, the dose is 40 times the dose of firstphosphorus doping, that is, 2×10¹⁵ atoms/cm². An accelerating voltage is80 kV. As a result, regions (source/drain) 1612 into which phosphorus isintroduced at a high concentration are formed. Also, low concentrationregions (LDDs) 1613 remain under the side walls. (FIG. 13E)

Further, a KrF excimer laser (wavelength of 248 nm and pulse width of 20ns) is irradiated to activate the doped impurity. A suitable energydensity of a laser is 200 to 400 mJ/cm², preferably 250 to 300 mJ/cm².

A silicon oxide film having a thickness of 5000 Å is formed as aninterlayer insulator 1614 on a whole surface by CVD. Contact holes areformed in source and drain regions of a TFT, and then an aluminumelectrode 1615 and an aluminum electrode arrangement 616 in the secondlayer are formed. A thickness of the aluminum electrode arrangement isapproximately equal to that of the gate electrode/arrangement, and 4000to 6000 Å.

By the above process, an N-channel type TFT having LDDs are completed.In order to activate impurity regions, hydrogen annealing may be furtherperformed at 200 to 400° C. Since a step in an overlap portion which thesecond layer arrangement 1616 overlaps the gate electrode arrangement1605 has a small sloop by the side walls 1611, although a thickness ofthe second layer arrangement is approximately (nearly) equal to a gateelectrode/arrangement, disconnection in a step is not almost observed.(FIG. 13F)

[Embodiment 12]

FIGS. 14A to 14F show a twelfth embodiment. In the embodiment, assimilar to Embodiment 8, an N-channel type TFT having LDDs and a normalP-channel type TFT are formed on the same substrate. In figures, anN-channel type TFT is shown in a left side and a P-channel type TFT isshown in a right side.

A silicon oxide film is formed as a base oxide film 1702 on a substrate(Corning 7059) 1701. Island silicon semiconductor regions are formed andthen silicon oxide film 1703 is formed as a gate insulating film on thesilicon semiconductor regions. An aluminum film having a thickness of5000 Å is formed to obtain gate electrodes 1704 and 1705. The gateelectrodes 1704 and 1705 are covered with anodic oxides.

Also, a gate oxide film in an N-channel type TFT is selectively removedby using the gate electrode 1704 as a mask, to expose a semiconductorlayer. Then, a silicon nitride film 1706 having a thickness of 100 to2000 Å, preferably 200 to 1000 Å, for example, 600 Å, is formed byplasma CVD.

By ion doping, phosphorus (P) is implanted using a gate electrodeportion as a mask, to form low concentration N-type impurity regions1707. A dose is 1×10¹³ atoms/cm². Accelerating voltage is 20 kV. In thisdoping process, since an accelerating voltage is low, phosphorus is notdoped into an island region 1708 in a P-channel type TFT covered withthe gate insulating film 1703. (FIG. 14A)

After an N-channel type TFT is masked by a photoresist 1709, boron (B)having a high concentration is doped by ion doping. A dose is 5×10¹⁴atoms/cm². An accelerating voltage is 65 kV. As a result, a P-typeimpurity regions 710 are formed in the island region 708. (FIG. 14B)

In the embodiment, a partial selective doping with a high concentrationboron is performed after a whole doping with a low concentrationphosphorus. However, a whole doping with a low concentration phosphorusmay be performed after a partial selective doping with a highconcentration boron.

After the photoresist 1709 as a mask is removed, a silicon oxide film1711 having a thickness of 4000 to 8000 Å is deposited by plasma CVD.(FIG. 14C)

As similar to Embodiment 8, by anisotropy etching, side walls 1712 and1713 of a silicon oxide are formed on side surfaces of the gateelectrodes. (FIG. 14D)

By ion doping, phosphorous (P) is introduced again. It is preferred thata dose is larger 1 to 3 orders (figures) than that in the process ofFIG. 14A. In the embodiment, the dose is 200 times the dose of firstphosphorus doping, that is, 2×10¹⁵ atoms/cm². An accelerating voltage is20 kV. As a result, regions (source/drain) 1714 into which phosphorus isintroduced at a high concentration are formed. Also, low concentrationimpurity regions (LDDs) 1715 remain under the side walls.

On the other hand, in the P-channel type TFT, since the gate insulatingfilm is formed, phosphorus ion is not implanted. In Embodiment 8, sincephosphorus and boron are implanted at a high concentration in aP-channel type TFT, a dose range is limited. In the embodiment, a doserange is not limited. However, it is desired that a dose of phosphorusis low and a dose of boron is high. (FIG. 14E)

After the doping process, a KrF excimer laser (wavelength of 248 nm andpulse width of 20 ns) is irradiated to activate the doped impurity. Asuitable energy density of a laser is 200 to 400 mJ/cm², preferably 250to 300 mJ/cm².

As shown in FIG. 14F, a silicon oxide film having a thickness of 5000 Åis formed as an interlayer insulator 1716 on a whole surface by CVD.Contact holes are formed in source and drain regions of a TFT, and thenaluminum electrode arrangements 1717, 1718, 1719 and 1720 are formed. Bythe above process, a semiconductor integrated circuit using an N-channeltype TFT having LDDs are completed.

In the embodiment, in comparison with Embodiment 2, a photolithographyprocess and an etching process are further performed to remove the gateoxide film in the N-channel type TFT. However, an N-type impurity is notintroduced substantially into the P-channel type TFT, it is merit that adose of N type and P-type impurities is can be changed easily.

Also, since phosphorus implanted into the vicinity of a surface of thegate insulating film 1703 in the P-channel type TFT is used to form aglass containing phosphorus by a later laser irradiating process, it iseffective in preventing entering of an active ion such as sodium.

[Embodiment 13]

FIGS. 15A to 15G show a thirteenth embodiment. The embodiment relates toa method for forming an active matrix type liquid crystal displaydevice. In figures, an N-channel type TFT having LDDs. (center portion)and a normal P-channel type TFT (left side) are logical circuits used ina peripheral circuit and the like, and a P-channel type TFT havingoffsets (right side) is a switching transistor used in an active matrixarray. A silicon oxide film is formed as a base oxide film on asubstrate (Corning 7059). Island silicon semiconductor regions (anisland region 1801 for a peripheral circuit and an island region 1802for an active matrix circuit) are formed and then silicon oxide film1803 is formed as a gate insulating film on the silicon semiconductorregions. An aluminum film (a thickness of 5000 Å) is formed to obtaingate electrodes 1804 and 1805 for a peripheral circuit and a gateelectrode 1806 for an active matrix circuit, which are covered withanodic oxides.

The gate insulating film of the P-channel type TFT for a peripheralcircuit and an active matrix circuit is selectively removed using thegate electrodes 1804 and 1806 as masks to expose the semiconductorregions. Also, by plasma CVD, a silicon nitride film 1807 having athickness of 100 to 2000 Å, preferably 200 to 1000 Å, for example, 400Å, is formed.

An active matrix circuit region is masked by a photoresist 1808 and thenboron is implanted using a gate electrode portion as a mask by iondoping, to form high concentration P-type impurity regions 1809. A doseis 1×10¹⁵ atoms/cm², and an accelerating voltage is 20 keV. In thisdoping process, since an accelerating voltage is low, boron is not dopedinto the N-channel type TFT covered with the gate insulating film 1803.(FIG. 15A)

After that, phosphorus is doped at a low concentration by ion doping. Adose is 1×10¹³ atoms/cm², and an accelerating voltage is 80 kV. As aresult, low concentration N-type impurity regions 1810 are formed in theN-channel type TFT. (FIG. 15B)

In FIG. 15B, doping is performed after the photoresist 1808 as a mask isremoved. Doping may be performed without removing the photoresist. Sincean accelerating voltage with respect to phosphorus is high, when thedoping is performed without removing the photoresist, phosphorus is notimplanted into the active matrix circuit region. Therefore, an idealP-channel type TFT having an offset is obtained. However, since thephotoresist is ashed by doping, removing of the photoresist takes timein a case.

When the photoresist is removed, since an accelerating voltage withrespect to phosphorus is high, a concentration peak of phosphorusproduces in a portion under the island semiconductor regions. However,it cannot be assured that phosphorus is not doped completely into theisland semiconductor regions, so that phosphorus having an extremelysmall quantity is introduced into the island semiconductor regions. Eventhough phosphorus is doped in this state, a concentration of phosphorusis less. This is preferred in a TFT for an active matrix circuit whichhas P⁺ (source)/n⁻/I (channel)/n⁻/P⁺ (drain) and is required to decreasea leak current.

After that, a silicon oxide film having a thickness of 4000 to 8000 Å isdeposited by plasma CVD. Further, as similar to Embodiment 8, byanisotropy etching, side walls 1811, 1812 and 1813 of a silicon oxideare formed on side surfaces of the gate electrodes. (FIG. 15C)

By ion doping, boron is introduced again. It is desired that a dose isapproximately equal to that of the process of FIG. 15A. In theembodiment, the dose is 1×10¹⁵ atoms/cm², and an accelerating voltage is20 keV. Since an accelerating voltage is low, boron is not doped intothe N-channel type TFT on which the gate insulating film 1803 is formed,so that boron is mainly doped into source and drain regions of theP-channel type TFTs for a peripheral circuit and an active matrixcircuit. As a result, source and drain regions 1814 of a TFT for anactive matrix circuit are formed. This TFT has an offset structure inwhich the gate electrode is spaced apart from the source and drainregions. (FIG. 15D)

Next, phosphorous is introduced. It is preferred that a dose is larger 1to 3 orders (figures) than that in the first phosphorus doping processof FIG. 15B. In the embodiment, the dose is 50 times the dose of thefirst phosphorus doping, that is, 5×10¹⁴ atoms/cm². An acceleratingvoltage is 80 kV. As a result, regions (source/drain) 1815 into whichphosphorus is introduced at a high concentration are formed. Also, lowconcentration regions (LDDs) 816 remain under the side walls. On theother hand, since phosphorus ion is almost implanted into a base film inthe P-channel type TFT, phosphorus does not influence a conductivitytype. (FIG. 15E)

After the doping process, a KrF excimer laser (wavelength of 248 nm andpulse width of 20 ns) is irradiated to activate the doped impurity. Asuitable energy density of a laser is 200 to 400 mJ/cm², preferably 250to 300 mJ/cm².

A silicon nitride film having a thickness of 5000 Å is formed as a firstinterlayer insulator 1817 on a whole surface by CVD. Contact holes areformed in source and drain regions of a TFT, and then aluminum electrodearrangements 1818, 1819, 1820 and 1821 are formed. By the above process,a peripheral circuit region is formed. (FIG. 15F)

Further, a silicon oxide film having a thickness of 3000 Å is formed asa second interlayer insulator 1822 by CVD. Contact holes are formed byetching the silicon oxide film, and then a pixel electrode 1823 isformed using a transparent conductive film in a TFT for an active matrixcircuit. By the above process, an active matrix type liquid crystaldisplay substrate is produced. (FIG. 15G)

By the present invention, the frequency of disconnection the secondlayer arrangement in an overlap portion of a gate electrode/arrangementcan be decreased. Though an integrated circuit is constructed by a lotof elements and arrangements, if a defect produces in a circuit, a wholecircuit may be not operated. Therefore, decrease of the number of defectpotions by the present invention produces superior effects in increaseof good product rate of an integrated circuit.

Also, by the present invention, a thickness of the second layerarrangement can be approximately equal to that of a gateelectrode/arrangement, that is, (the thickness of the gateelectrode/arrangement) ±1000 (Å). This is preferred in an active matrixcircuit of a liquid crystal display device for which a substrate havingan even surface is required, The present invention is useful inimproving a yield of a TFT integrated circuit.

What is claimed is:
 1. A semiconductor device comprising an n-channeltype thin film transistor and a p-channel type thin film transistor,each comprising: a semiconductor film formed over a substrate having aninsulating surface; a pair of source and drain regions in saidsemiconductor film; a channel region in said semiconductor film; and agate insulating film adjacent to said channel region and a gateelectrode adjacent to said channel region with said gate insulating filminterposed therebetween, wherein said n-channel type thin filmtransistor has at least one lightly doped region between said channelregion and at least one of said source and drain regions, wherein saidp-channel type thin film transistor has no lightly doped region betweensaid channel region and either of said source and drain regions in saidsemiconductor film, and wherein said lightly doped region has a doseamount between 1×10¹³ and 5×10¹⁴ atoms/cm².
 2. A semiconductor deviceaccording to claim 1 wherein the gate electrode is located over thechannel region in each of the n-channel type thin film transistor andthe p-channel type thin film transistor.
 3. A semiconductor deviceaccording to claim 1 wherein said p-channel type thin film transistor iscomplementarily connected to said n-channel type thin film transistor.4. A semiconductor device according to claim 1 wherein saidsemiconductor device is one selected from the group consisting of adriver circuit, a central processing unit, a random access memory, adecoder driver, a correction memory and an input port.
 5. Asemiconductor device comprising an n-channel type thin film transistorand a p-channel type thin film transistor, each comprising: asemiconductor film formed over a substrate having an insulating surface;a pair of source and drain regions in said semiconductor film; a channelregion in said semiconductor film; and a gate insulating film adjacentto said channel region and a gate electrode adjacent to said channelregion with said gate insulating film interposed therebetween, whereinsaid n-channel type thin film transistor has at least one lightly dopedregion between said channel region and at least one of said source anddrain regions, wherein said p-channel type thin film transistor has nolightly doped region between said channel region and either of saidsource and drain regions in said semiconductor film, and said source anddrain regions are doped with both phosphorus and boron, and wherein saidlightly doped region has a dose amount between 1×10¹³ and 5×10¹⁴atoms/cm.
 6. A semiconductor device according to claim 5 wherein thegate electrode is located over the channel forming region in each of then-channel type thin film transistor and the p-channel type thin filmtransistor.
 7. A semiconductor device according to claim 5 wherein saidp-channel type thin film transistor is complementarily connected to saidn-channel type thin film transistor.
 8. A semiconductor device accordingto claim 5 wherein said semiconductor device is one selected from thegroup consisting of a driver circuit, a central processing unit, arandom access memory, a decoder driver, a correction memory and an inputport.
 9. A semiconductor device comprising an n-channel type thin filmtransistor and a p-channel type thin film transistor, each comprising: asemiconductor film formed over a substrate having an insulating surface;a gate insulating film formed on said semiconductor film; a pair ofimpurity regions formed in said semiconductor film; a channel regionformed in said semiconductor film between said pair of impurity regions;a gate electrode formed over the channel region with said gateinsulating film interposed therebetween; and a second insulating filmcomprising silicon nitride formed on said gate insulating film and saidgate electrode, wherein said n-channel type thin film transistor has atleast one lightly doped region disposed between said channel region andat least one of said pair of impurity regions, and said p-channel typethin film transistor has no lightly doped region between said channelregion and either of said pair of impurity regions, wherein said gateinsulating film and said second insulating film cover said semiconductorfilm except for contact holes opened therein, and wherein said lightlydoped region has a dose amount between 1×10¹³ and 5×10¹⁴ atoms/cm². 10.A semiconductor device according to claim 9 wherein said semiconductordevice is one selected from the group consisting of a driver circuit, acentral processing unit, a random access memory, a decoder driver, acorrection memory and an input port.
 11. A semiconductor devicecomprising an n-channel type thin film transistor and a p-channel typethin film transistor, each comprising: a semiconductor film formed overa substrate having an insulating surface; a gate insulating film formedon said semiconductor film; a pair of impurity regions formed in saidsemiconductor film; a channel region formed in said semiconductor filmbetween said pair of impurity regions; a gate electrode formed over thechannel region with said gate insulating film interposed therebetween;and a second insulating film formed on said gate insulating film andsaid first and second gate electrodes, wherein said n-channel type thinfilm transistor has at least one lightly doped region disposed betweensaid channel region and at least one of said pair of impurity regions,and said p-channel type thin film transistor has no lightly doped regionbetween said channel region and either of said pair of impurity regions,wherein said gate insulating film and said second insulating film coversaid semiconductor film except for contact holes opened therein, andwherein said lightly doped region has a dose amount between 1×10¹³ and5×10¹⁴ atoms/cm².
 12. A semiconductor device according to claim 11wherein said semiconductor device is one selected from the groupconsisting of a driver circuit, a central processing unit, a randomaccess memory, a decoder driver, a correction memory and an input port.13. A semiconductor device having an active matrix circuit comprising aplurality of switching elements formed over a substrate for switchingpixels; and a driver circuit for driving said active matrix circuit,said driver circuit comprising an n-channel type thin film transistorand a p-channel type thin film transistor, each comprising: asemiconductor film formed over said substrate having an insulatingsurface; a pair of source and drain regions in said semiconductor film;a channel region in said semiconductor film; and a gate insulating filmadjacent to said channel region and a gate electrode adjacent to saidchannel region with said gate insulating film interposed therebetween,wherein said n-channel type thin film transistor has at least onelightly doped region between said channel region and at least one ofsaid source and drain regions, wherein said p-channel type thin filmtransistor has no lightly doped region between said channel region andeither of said source and drain regions in said semiconductor film, andwherein said lightly doped region has a dose amount between 1×10¹³ and5×10¹⁴ atoms/cm².
 14. A semiconductor device according to claim 13wherein the gate electrode is located over the channel forming region ineach of the n-channel type thin film transistor and the p-channel typethin film transistor.
 15. A semiconductor device according to claim 13wherein said p-channel type thin film transistor is complementarilyconnected to said n-channel type thin film transistor.
 16. Asemiconductor device having an active matrix circuit comprising aplurality of switching elements formed over a substrate for switchingpixels; and a driver circuit for driving said active matrix circuit,said driver circuit comprising an n-channel type thin film transistorand a p-channel type thin film transistor, each comprising: asemiconductor film formed over said substrate having an insulatingsurface; a pair of source and drain regions in said semiconductor film;a channel region in said semiconductor film; and a gate insulating filmadjacent to said channel region and a gate electrode adjacent to saidchannel region with said gate insulating film interposed therebetween,wherein said n-channel type thin film transistor has at least onelightly doped region between said channel region and at least one ofsaid source and drain regions, wherein said p-channel type thin filmtransistor has no lightly doped region between said channel region andeither of said source and drain regions in said semiconductor film, andsaid source and drain regions are doped with both phosphorus and boron,and wherein said lightly doped region has a dose amount between 1×10¹³and 5×10¹⁴ atoms/cm².
 17. A semiconductor device according to claim 16wherein the gate electrode is located over the channel forming region ineach of the n-channel type thin film transistor and the p-channel typethin film transistor.
 18. A semiconductor device according to claim 16wherein said p-channel type thin film transistor is complementarilyconnected to said n-channel type thin film transistor.
 19. Asemiconductor device having an active matrix circuit comprising aplurality of switching elements formed over a substrate for switchingpixels; and a driver circuit for driving said active matrix circuit,said driver circuit comprising an n-channel type thin film transistorand a p-channel type thin film transistor, each comprising: asemiconductor film formed over said substrate having an insulatingsurface; a gate insulating film formed on said semiconductor films; apair of impurity regions formed in said semiconductor film; a channelregion formed in said semiconductor film between said pair of impurityregions; a gate electrode formed over the channel region with said gateinsulating film interposed therebetween; and a second insulating filmcomprising silicon nitride formed on said gate insulating film and saidgate electrode, wherein said n-channel type thin film transistor has atleast one lightly doped region disposed between said channel region andat least one of said pair of impurity regions, and said p-channel typethin film transistor has no lightly doped region between said channelregion and either of said pair of impurity regions, wherein said gateinsulating film and said second insulating film cover said semiconductorfilm except for contact holes opened therein, and wherein said lightlydoped region has a dose amount between 1×10¹³ and 5×10¹⁴ atoms/cm². 20.A semiconductor device having an active matrix circuit comprising aplurality of switching elements formed over a substrate for switchingpixels; and a driver circuit for driving said active matrix circuit,said driver circuit comprising an n-channel type thin film transistorand a p-channel type thin film transistor, each comprising: asemiconductor film formed over said substrate having an insulatingsurface; a gate insulating film formed on said semiconductor films; apair of impurity regions formed in said semiconductor film; a channelregion formed in said semiconductor film between said pair of impurityregions; a gate electrode formed over the channel region with said gateinsulating film interposed therebetween; and a second insulating filmformed on said gate insulating film and said gate electrode, whereinsaid n-channel type thin film transistor has at least one lightly dopedregion disposed between said channel region and at least one of saidpair of impurity regions, and said p-channel type thin film transistorhas no lightly doped region between said channel region and either ofsaid pair of impurity regions, wherein said gate insulating film andsaid second insulating film cover said semiconductor film except forcontact holes opened therein, and wherein said lightly doped region hasa dose amount between 1×10¹³ and 5×10¹⁴ atoms/cm².
 21. A semiconductordevice according to claim 1 further comprising an anodic oxide film onsaid gate electrode; and a substantially triangular insulator adjacentto a side surface of said gate electrode, wherein said lightly dopedregion is provided under said substantially triangular insulator.
 22. Asemiconductor device according to claim 5 further comprising an anodicoxide film on said gate electrode; and a substantially triangularinsulator adjacent to a side surface of said gate electrode, whereinsaid lightly doped region is provided under said substantiallytriangular insulator.
 23. A semiconductor device according to claim 9further comprising an anodic oxide film on said gate electrode; and asubstantially triangular insulator adjacent to a side surface of saidgate electrode, wherein said lightly doped region is provided under saidsubstantially triangular insulator.
 24. A semiconductor device accordingto claim 11 further comprising an anodic oxide film on said gateelectrode; and a substantially triangular insulator adjacent to a sidesurface of said gate electrode, wherein said lightly doped region isprovided under said substantially triangular insulator.
 25. Asemiconductor device according to claim 13 further comprising an anodicoxide film on said gate electrode; and a substantially triangularinsulator adjacent to a side surface of said gate electrode, whereinsaid lightly doped region is provided under said substantiallytriangular insulator.
 26. A semiconductor device according to claim 16further comprising an anodic oxide film on said gate electrode; and asubstantially triangular insulator adjacent to a side surface of saidgate electrode, wherein said lightly doped region is provided under saidsubstantially triangular insulator.
 27. A semiconductor device accordingto claim 19 further comprising an anodic oxide film on said gateelectrode; and a substantially triangular insulator adjacent to a sidesurface of said gate electrode, wherein said lightly doped region isprovided under said substantially triangular insulator.
 28. Asemiconductor device according to claim 20 further comprising an anodicoxide film on said gate electrode; and a substantially triangularinsulator adjacent to a side surface of said gate electrode, whereinsaid lightly doped region is provided under said substantiallytriangular insulator.
 29. A semiconductor device according to claim 11wherein said second insulating film comprises silicon nitride.
 30. Asemiconductor device according to claim 20 wherein said secondinsulating film comprises silicon nitride.